I am interested in the mechanisms by which hormones and growth factors, which exert their actions through binding to cell surface receptors, are able to control the expression of specific genes. The interferons are included in this group of growth regulators and provide an attractive model to study the induction of new gene activity. An understanding of the mechanisms by which the interferons regulate the expression of certain genes should provide more insight into the pleiotropic effects of these proteins. During the past four years, I have isolated two cDNAs which correspond to two mRNAs whose expression is induced in an all or none fashion by type I interferons in a variety of human cultured cells. The induction of these mRNAs is mediated by an increase in the rate of transcription of these genes. The regulation of the transcription of the genes is complex, and involves both positive factors whose expression does not require new protein synthesis, and negative elements which inhibit the expression of these genes in certain types of cells after prolonged exposure to interferon. The action of these negative regulatory factors requires the synthesis of new proteins. Recently, I and others have isolated and characterized the regulatory regions of interferon-sensitive genes. The availability of the cDNAs (mentioned above) and the regulatory regions of these interferon-induced genes has allowed a more detailed investigation of the expression of these mRNAs to be initiated.